The present invention relates to a binder for a gas generating material. The gas generating material is particularly useful for inflating a vehicle occupant protection device.
An inflatable vehicle occupant protection device, such as an air bag, is inflated by gas provided by an inflator. The inflator contains a gas generating material. The inflator further includes an igniter. The igniter is actuated to ignite the gas generating material when the vehicle experiences a collision for which inflation of the air bag is desired. As the gas generating material burns, it generates a volume of inflation gas. The inflation gas is directed into the air bag to inflate the air bag. When the air bag is inflated, it expands into the vehicle occupant compartment and helps to protect the vehicle occupant.
A typical gas generating material for use in an inflator for inflating a vehicle occupant protection device includes a particulate oxidizer and a particulate fuel bound into a solid mass by a binder. A variety of binders are known for binding a particulate oxidizer and a particulate fuel into a solid mass.
The mechanical properties of the binder are critical. The binder must form a solid mass with the particulate oxidizer and the particulate fuel that can satisfactorily ignite and combust over the range of expected operating conditions. The binder must be flexible at temperatures down to about xe2x88x9240xc2x0 C. and resistant to creep at temperatures up to about 110xc2x0 C.
The present invention is a gas generating material that comprises an oxidizer, a fuel, and a binder. The binder includes a polystyrene based thermoplastic block copolymer and a thermoplastic modifier. The thermoplastic modifier is miscible with the polystyrene based thermoplastic block copolymer and has a glass transition temperature greater than about 170xc2x0 C.